... and gas fee, balance notice, etc.. TM100 GSM Data Transmission Unit (DTU), GSM SMS Modem Brief Descriptions:TM100 DTU is a wireless Data ... Transmission Unit (DTU) based on GSM network, it uses ... of Tri-frequency GSM900/1800/1900 MHz(or quad-frequency GSM 850/900/1800/1900MHz);Support SMS, DTMF;Data GPRS: GPRS ...